A long wire is known to have a radius greater than 5.6 mm and to carry a current that is uniformly distributed over its cross section. The magnitude of the magnetic field due to that current is 0.57 mT at a point 4.0 mm from the axis of the wire, and 0.33 mT at a point 42 mm from the axis of the wire. What is the radius (in mm) of the wire?